Power steering system for vehicle

ABSTRACT

The power steering system for a vehicle includes a steering wheel, a torsion bar fixed to the steering wheel to rotate therewith, a hydraulic control unit for controlling hydraulic pressure generating from an oil pump in accordance with the rotation of the torsion bar, the hydraulic control unit being mounted around the torsion bar, and a power cylinder separated from the torsion bar and receiving the hydraulic pressure from the hydraulic control unit, the power cylinder having a piston meshed with a sector gear which is connected with a pitman arm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power steering system for a vehicleand, more particularly, to a power steering system which can adjust theposition of wheels of the vehicle by means of only hydraulic pressurewithout a steering shaft thereby enlarging a space for a driver.

2. Description of Related Art

Generally, in case of using low pressure tires, since adhesion force ofsteerable wheels is increased, a large force for handling the steeringwheel is required to steer the vehicle rapidly. In recent years, since afront wheel drive car and a wide width tire have become quite popular,the power steering system is used to accomplish the rapid steeringoperation and to provide the low handling force.

The power steering system is designed to reduce the force for handlingthe steering wheel by receiving the hydraulic pressure from an oil pumpwhich is operated by an engine.

In a conventional power steering system, as shown in FIG. 12, a columnshaft assembly 102 is supported on a bracket 101 mounted toward adriver's seat and a steering wheel 104 is fixed to a steering shaft 103which extends from an upper end of the column shaft assembly 102.Further, a power cylinder 105 is connected to a lower end of thesteering shaft 103 by means of a universal joint 106 such that thesteering force of the steering wheel 104 is transmitted to the powercylinder 105.

The power steering system is designed such that the hydraulic pressuregenerated from the oil pump is induced to the power cylinder 105. Thedirection of the hydraulic pressure is changed in accordance with thesteering direction, whereby a piston (not shown) within the powercylinder is moved by the hydraulic pressure.

However, in the power steering system, since the mounting angle betweenthe column shaft assembly and the power cylinder should be maintained ata predetermined angle, it is difficult to set a layout of the vehicle.

Particularly, since the column shaft and the universal joint aredisposed toward the driver's seat, the space for the driver is reduced.Further, a plurality of supporting members should be used for fixing thecolumn shaft assembly which increase the manufacturing cost.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in an effort to solve theabove-described problems.

It is an object of the present invention to provide a power steeringsystem which can reduce the manufacturing cost and enlarge the space fordriver by mounting a hydraulic control unit part and a power cylinder tobe separated from each other.

To achieve the above object, the present invention provides a powersteering system for a vehicle comprising a steering wheel; a torsion barfixed to the steering wheel to rotate therewith; a hydraulic controlunit for controlling hydraulic pressure generating from an oil pump inresponse to the rotation of the torsion bar, the hydraulic control unitbeing mounted around the torsion bar; and a power cylinder separatedfrom the torsion bar and receiving the hydraulic pressure from thehydraulic control unit, the power cylinder having a piston meshed with asector gear connected with a pitman arm.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and other advantages of the invention will becomeapparent from the following description in conjunction with the attacheddrawings, in which:

FIG. 1 is a schematic view of a power steering system in accordance witha preferred embodiment of the present invention;

FIG. 2 is a sectional view of a hydraulic control unit of the powersteering system in accordance with the preferred embodiment of thepresent invention;

FIG. 3 is a partially cutaway perspective view of a valve assembly forforming the hydraulic control unit in accordance with the preferredembodiment of the present invention;

FIG. 4 is a plan view of a first rotating member of the hydrauliccontrol unit in accordance with the preferred embodiment of the presentinvention;

FIG. 5 is a transverse cross section view of a second rotating member ofthe hydraulic control unit in accordance with the preferred embodimentof the present invention;

FIG. 6 is a transverse cross section view of a third rotating member ofthe hydraulic control unit in accordance with the preferred embodimentof the present invention;

FIG. 7A is a plan view for showing the second rotating member;

FIG. 7B is a sectional view taken along lines 7B--7B of FIG. 7A;

FIG. 7C is a sectional view taken along lines 7C--7C of FIG. 7A;

FIG. 8 is a side sectional view of a power cylinder in accordance withthe preferred embodiment of the present invention;

FIG. 9A is a view for illustrating operation of the power steeringsystem in accordance with the present invention;

FIG. 9B is a view for illustrating formation of the hydraulic passage inresponse to the rotation of the rotating members;

FIG. 10A is a view for showing the formation of the hydraulic passagewhere the first and second rotating members communicate with each otherwhen the vehicle makes a turn to the right;

FIG. 10B is a longitudinal view of FIG. 10A;

FIG. 11A is a view for showing the formation of the hydraulic passagewhere the second and fourth rotating members communicate with each otherwhen the vehicle makes a turn to the left;

FIG. 11B is a longitudinal view of FIG. 11A; and

FIG. 12 is a view of a conventional power steering system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a power steering system in accordance with a preferredembodiment of the present invention. The power steering system isdesigned such that a hydraulic control unit part 2 and a power cylinder4 are separated from each other and connected with each other through afluid tube 6 to actuate the power cylinder with only a hydraulicpressure.

The hydraulic control unit part 2 includes a torsion bar 8 on an upperend of which a steering wheel 10 is mounted. The power cylinder 4includes a pitman arm 12 which is mechanically connected to a wheelcarrier by means of a drag link 14.

FIGS. 2 and 3 are a sectional view and a partly cutaway perspective viewfor illustrating the hydraulic control unit part 2, respectively. Thehydraulic control unit part 2 further comprises a first rotating member18 which is connected to a lower end of the torsion bar 8 by a pin 16 toreceive a rotation force of the steering wheel 10, second and thirdrotating members 20 and 22 which receive the rotation force from thefirst rotating member 18, and a fourth rotating member 24 which receivesthe rotation force from the second and third rotation members 20 and 22.

The first rotating member 18 is integrally formed with a cylindricalsleeve 26 in which the torsion bar 8 is inserted. The torsion bar 8 isfixed to a lower end of the sleeve 26 by the pin 16 and a lower end ofwhich is supported to a cap 30 through a bearing 28.

As shown in FIGS. 2, 3 and 4, the first rotating member 18 includesgrooves 34, 36, 38 and 40 formed on its flange 32, a hole 42 formed onits center through which the torsion bar 8 passes, pins 44 and 46 whichproject from its upper surface, and pins 78 and 80 projecting from itsbottom surface.

As shown in FIGS. 2, 3 and 5, the second rotating member 20 has grooves48 and 50 formed on its bottom surface to receive the pins 44 and 46,and vertical passages 52, 54, 56 and 58.

The vertical passages 52, 54, 56 and 58 communicate with a channel 60which is formed along an outer circumferential surface of the secondrotating member 20 such that oil can flow therethrough. Further, a screwthread 62 is formed along the outer circumferential surface of thesecond rotating member 20 and a circumferential groove 64 is formed onthe bottom surface of the second rotating member to receive ball members118.

The third rotating member 22, as shown in FIGS. 2, 3 and 6, includes acircumferential groove 66, aligned to the circumferential groove 64 ofthe second rotating member 20 and formed on its upper surface, a channel68 formed along its outer circumferential surface, and vertical passages70, 72, 74, and 76 communicating with the channel 68.

Further, the third rotating member 22 is provided with grooves 82 and 84having a predetermined length to receive pins 78 and 80 which are formedon the bottom surface of the first rotating member 18.

When the steerable wheels are in a straight position longitudinallyaligned with the vehicle body, the pins 44 and 46 which are received inthe grooves 48 and 50 and the pins 78 and 80 which are received in thegrooves 82 and 84 are displaced as shown in FIG. 9A.

As shown in FIGS. 7A to 7C, the fourth rotating member 24 includes upperhorizontal passages 86, 88, 90 and 92 and lower horizontal passages 94,96, 98 and 100, all of which can selectively communicate with thegrooves 34, 36, 38 and 40 of the first rotating member.

The upper horizontal passages 86, 88, 90 and 92 communicate with an oilpump (not shown) to receive the oil required for steering. The lowerhorizontal passages 94, 96, 98 and 100 are passages for returning theoil to a reservoir tank (not shown).

The upper and lower horizontal passages are angularly offset from eachother along the circumference when viewed from the plan view as shown inFIG. 9B. However, in a straight ahead position, each inner end of theupper and lower horizontal passages communicates with the grooves 34,36, 38 and 40 of the first rotating member 18 such that the oilgenerated from the oil pump flows into the upper horizontal passages 86,88, 90 and 92 and then flows out to the lower horizontal passages 94,96, 98 and 100 via the grooves 34, 36, 38 and 40, respectively.

Further, the fourth rotating member 24 has vertical passages 102, 104,106 and 108 which communicate with the vertical passages 52, 54, 56 and58 of the second rotating member and the vertical passages 70, 72, 74and 76 of the third rotating member.

Pins 110 and 112 are formed on an upper surface of the fourth rotatingmember 24 and are located in grooves 111 and 113 formed on a bottomsurface of the second member, respectively. Further, pins 114 and 116are formed on a bottom surface of the fourth rotating member and arelocated in grooves 115 and 117 formed on an upper surface of the thirdrotating member, respectively.

Ball members 118 are provided between the faces of the first, second,third and fourth rotating members 18, 20, 22 and 24 to aid smoothrotation. A screw thread 120 is formed on an outer circumferentialsurface of the third rotating member 22.

As shown in FIG. 2, the lower cap 30 is screw coupled to the lowerportion of the cylinder 122. An upper cap 124 is also coupled to theupper portion of the cylinder 122. The first, second, third and fourthrotation members are disposed between the upper and lower caps 30 and124 and the second and third rotating members are screw coupled to aninner circumferential surface of the cylinder 122.

The cylinder 122 is provided with holes 126 and 128 formed on its oneside and holes 130 and 132 which communicate with the channel 60 of thesecond rotating member and the channel 68 of the third rotating member,respectively.

In order to communicate with upper and lower horizontal passages of thefourth rotating member 24 with the holes 126 and 128 of the cylinder122, respectively, channels 133 and 134 are formed along the outercircumferential surfaces of the upper and lower horizontal passages ofthe fourth rotating member 24.

FIG. 8 is a side sectional view for illustrating a power cylinder 4 ofthe present invention. The power cylinder includes a housing 136. Thehousing 136 is provided with intake ports 138 and 140 connected withfluid tubes 6a and 6b, respectively, and exhaust ports 142 and 144opposite to intake ports 138 and 140, respectively.

Check valves 146 and 148 are mounted between the ports 138 and 142 andthe ports 140 and 144, respectively, to supply the oil to the chambers150 and 152 or exhaust the oil from the chambers 150 and 152.

A piston 154 is mounted in the housing 136 such that when the oil flowsinto one of the chambers 150 and 152, the piston 154 can move in adirection. A rack gear 156 is integrally formed on the piston and inmesh with a sector gear 158 coupled with the pitman arm 12.

In the power steering system as described above, when the steering wheel10 is in a neutral position, the hydraulic control unit part 2 maintainsits state as shown in FIGS. 2, 9A and 9B.

The grooves 34, 36, 38 and 40 of the first rotating member 18 aredisposed to communicate with the upper and lower horizontal passages ofthe fourth rotating member 24.

Accordingly, the oil transmitted from the oil pump during the engineoperation flows into the hole 126 of the cylinder 122 and then issupplied to the channel 133 of the fourth rotating member 24 therebyflowing along the upper horizontal passages 86, 88, 90 and 92.

By this flow, the oil flows into the grooves 34, 36, 38 and 40 of thefirst rotating member 18 and, at this point, since the grooves 34, 36,38 and 40 communicate with the lower horizontal passages 94, 96, 98 and100, the oil returns to the reservoir tank through the holes 128 of thecylinder 122.

At this point, as shown in FIGS. 9A and 9B, the pins 44 and 46 fixed onthe first rotating member 18 are to be located in the grooves 48 and 50of the second rotating member 20 and are designed to rotate the secondrotating member 20 in the clockwise direction if the first rotatingmember rotates in the clockwise direction. And, the pins 78 and 80 fixedon the bottom surface of the first rotating member 18 and located in thegrooves 82 and 84 of the third rotating member 22, respectively, aredesigned to rotate the third rotating member in the counter-clockwisedirection if the first rotating member 18 rotates in thecounter-clockwise direction.

In this state, when turning the steering wheel to the right, the torsionbar 8 fixed to the steering wheel rotates therewith to rotate the firstrotating member 18.

As a result, the pins 44 and 46 of the first rotating member 18 rotatethe second rotating member 20 and, at this point, the pins 78 and 80received in the grooves 82 and 84, respectively, cannot rotate the thirdrotating member 22 until the pins 78 and 80 contact one side of eachgroove. Therefore, from the moment each pin 78 and 80 contacts the oneside of each groove, the third rotating member rotates. When thesteering wheel further turns to the right, the grooves 34, 36, 38 and 40of the first rotating member 18 are slowly closed. And then, the grooves52, 54, 56, 58 of the second rotating member 20 become respectivelycorresponding to the grooves 102, 104, 106 and 108 of the fourthrotating member 24 to communicate with each. At this point, since eachpin 110 and 112 of the fourth rotating member 24 contacts the sides ofthe grooves 111 and 113 of the second rotating member 20, the first,second and fourth rotating members 18, 20 and 24 integrally rotate.

That is, the first, second and fourth rotating members 18, 20 and 24rotate simultaneously such that the grooves 115 and 117 of the thirdrotating member 22 contact the pins 114 and 116, respectively, to rotatewith the first, second and fourth rotating members 18, 20 and 24.

If a driver further turns the rotating wheel to the right, the secondand third rotating members 20 and 22 which are screw coupled to thecylinder 122 rotate along the screw thread of the cylinder to moveupward and downward, thereby providing a steering sensitivity. At thispoint, the springs 202 and 204 elastically supporting the second andthird rotating member, respectively absorb the movement of the rotatingmembers. The bearings 302 and 304 between the upper and lower caps 124and 30 and the second and third rotating members 20 and 24,respectively, permit the rotating members to smoothly rotate.

As a result, the second rotating member 20 is more rotated in thesteering direction of the steering wheel than the third rotating member22, such that the vertical passages 102, 104, 106 and 108 become incommunication with the passages 52, 54, 56 and 58 of the second rotatingmember 20 (see FIGS. 10A and 10B).

Further, since the vertical passages 102, 104, 106 and 108 still do notcommunicate with the vertical passages 70, 72, 74 and 76 of the thirdrotating member 22, the hydraulic pressure supplied from the oil pumpflows into the cylinder 122 through the hole 130 and then flows into theleft chamber 150 of the power cylinder 4 along the fluid tube 6a via thevertical passages of the fourth rotating member 24 and the verticalpassages of the second rotating member 20.

By this operation, the piston moves rightward in FIG. 8 and rotates thesector gear 158 meshed with the pitman arm 12, thereby making a turn tothe left.

As described above, in the steering system of the present invention,since the steering of the vehicle is accomplished without a steeringshaft, a space for the driver can be enlarged.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the pertinent artwill still fall within the spirit and scope of the appended claims.

What is claimed is:
 1. A power steering system for a vehicle,comprising:a rotatable mounted steering wheel; a torsion bar fixed tosaid steering wheel so as to rotate therewith; a hydraulic control unitfor controlling a hydraulic pressure from an oil pump in response to arotation of said torsion bar, said hydraulic control unit being mountedaround said torsion bar and comprising:a first rotating member forreceiving a rotating force from said torsion bar which is inserted intoand fixed to a central axle of said first rotating member, an outercircumference of said first rotating member having a plurality ofgrooves formed thereon; a second rotating member located around saidtorsion bar at an upper side of said first rotating member to receivethe rotating force from said first rotating member, an outercircumference of said second rotating member having a channel formedtherealong; a third rotating member located around said torsion bar at alower side of said first rotating member to receive the rotating forcefrom said first rotating member, an outer circumference of said thirdrotating member having a channel formed therealong; a fourth rotatingmember located at an outer circumference of said first rotating memberbetween said second and third rotating members and having a plurality ofupper and lower horizontal passages selectively communicating with saidplurality of grooves of said first rotating member, and a plurality ofvertical passages communicating with said channels of said second andthird rotating members, respectively; and a cylinder for containing saidfirst, second, third and fourth rotating members, said cylinder havingtwo holes each communicating with a respective said channel of saidsecond and third rotating members; and a power cylinder spaced from saidtorsion bar and receiving the hydraulic pressure from said hydrauliccontrol unit, said power cylinder having a piston meshed with a sectorgear which is connected with a pitman arm.
 2. The power steering systemof claim 1, wherein said upper horizontal passages are angularly indexedto said lower horizontal passages.
 3. The power steering system of claim2, wherein said plurality of grooves of said first rotating membercommunicate with said upper horizontal passages and said lowerhorizontal passages of said fourth rotating member when the vehicle issteered straight.
 4. The power steering system of claim 2, wherein saidplurality of grooves of said first rotating member selectivelycommunicate with said plurality of upper passages and said plurality oflower passages of said fourth rotating member when the vehicle issteered left or right.
 5. The power steering system of claim 1,comprising ball members provided on each contacting surface between saidfirst rotating member and second and third rotating members.
 6. Thepower steering system of claim 1, wherein said second and third rotatingmembers each have a plurality of vertical passages, respectively, whichselectively communicate with said plurality of vertical passages of saidfourth rotating member in response to a steering direction of thevehicle.
 7. The power steering system of claim 1, wherein said firstrotating member includes a sleeve connected with said torsion bar. 8.The power steering system of claim 1, wherein said power cylinder isprovided with intake and exhaust ports and a check valve between saidintake and exhaust ports.
 9. A power steering system for a vehicle,comprising:a hydraulic control unit including:a first rotating memberwhich rotates in response to a rotation of a steering wheel; second andthird rotating members which rotate with said first rotating membersimultaneously or in turn; and a fourth rotating member for supplying anoil to one of said first, second and third rotating members in responseto a rotation of said second and third rotating members; and a powercylinder for steering steerable wheels of the vehicle right or left bymoving a piston which is connected to the steerable wheels by way of adrag link and a pitman arm, said power cylinder being in hydrauliccommunication with said hydraulic control unit by two fluid tubes,whereby a movement of the piston is controlled by a hydraulic pressuresupplied from said hydraulic control unit.
 10. The power steering systemof claim 9, wherein said first member comprises a sleeve operativelyconnected with the steering wheel and includes more than two groovesformed along an outer circumference thereof.
 11. The power steeringsystem of claim 9, wherein said second rotating member includes morethan two vertical passages, and a channel formed along an outercircumference of said second rotating member and communicating with saidvertical passages.
 12. The power steering system of claim 9, whereinsaid third rotating member includes more than two vertical passages, anda channel formed along an outer circumference of said second rotatingmember and communicating with said vertical passages.
 13. The powersteering system of claim 9, wherein said fourth rotating member includesa channel for receiving hydraulic pressure from an oil pump, more thantwo horizontal passages communicating with said channel, and more thantwo vertical passages communicating with said horizontal passages, saidhorizontal passages being disposed on upper and lower portions of saidfourth rotating member, wherein one said horizontal passage disposed onsaid upper portion is angularly indexed to one said horizontal passagedisposed on said lower portion.
 14. The power steering system of claim9, wherein said power cylinder includes first and second intake ports,first and second exhaust ports, and first and second chambers defined bysaid piston, such that hydraulic pressure is selectively supplied to oneof said first and second chambers by opening one of said first andsecond intake ports.
 15. The power steering system of claim 9, whereinsaid second rotating member receives the rotating force by a first pinfixed on an upper surface of said first rotating member, said thirdrotating member receives rotating force by a second pin fixed on abottom surface of said first rotating member, said first and second pinsbeing received in grooves formed on a bottom surface of said secondrotating member and an upper surface of said third rotating member,respectively.